is a bit complicated so I've seen to update to android 7 the imei disappears, because they do not launch via ota the update? please so it would be easier

Dear David_ortiz98, indeed it is a bit more complicated, but it is way more safe. Corrupted downloads of OTA packages, missing space on the phone can lead to soft-bricks. And you would only have one try.

Did you loose your IMEI during flash? This most likely happens if users use the "Format all + Download" option. But it can be restored. Pardon me if I repeat this again: "PLEASE never choose Format all option for doing this, as it will destroy your NVRAM." The NVRAM holds the IMEI and hardware addresses.But it can easily be repaired by using Mediateks SN Writer Tool. Let me know, if you need help on this.